Primary cell



Ap 3, 1951 A. B. FRY ET An.

PRIMARY CELL Filed Jan. 27, 1949 Ir si. 5.

BY Percy E Geo/:ge

A TTQRNE YS Patented Apr; 3, `1951.

2,547,908 PRIMARY CELL Ashford B. Fry, Roy C. Kirk, and Percy F. George,

Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware Application January 27, 1949, Serial No. 73,064

(Cl. 13G- 100) l 14 Claims. lihe invention relates to an improvedprimary ce It more particularly concerns an improved primary cellutilizing as the anode material magnesium and alloys thereof in whichmagnesium is the predominant constituent.

Inasmuch as magnesium is an abundant and readily available metal high inthe electromotive force series of the metals, it is a desideratum in theart to employ it as the anode material in primary cells, and numerousattempts at such use have been made. Nevertheless, insofar as we areaware, there are no commercially successful primary cells employingmagnesium as anode material.

Accordingly, it is the principal object of the invention to provide animproved primary cell utilizing magnesium as the anode material, suchobject being attained by the means and in the manner described in thefollowing specification and illustrated in the annexed drawing.

In `said drawing:

Fig. 1 shows a cutaway isometric view of a wet cell assembled accordingto the invention:

Fig. 2 shows a vertical section of a "dry" cell embodying the invention.

In brief, the primary cell of the invention consists of a voltaic systememploying an anode of magnesium or alloy thereof in which magnesium isthe predominant material, a cathode of carbon depolarized with manganesedioxide, and an electrolyte of an aqueous solution of ammonium bro-.mide which may advantageously contain a chromic acid salt of one of thealkali, alkaline earth metal, or ammonium bases to modify the corrosiveaction of ammonium bromide upon magnesium.

Referring more specifically to the elements of the cell, the anodeV maybe formed of either pure metallic magnesium or of a magnesium-base alloycontaining a major portion of the metal, al1 such materials beingincluded with the term magnesium hereinafter employed. However.

metallic magnesium of at least 995 per centof manganese and either orboth aluminum and zinc. Suitable proportions of these alloying elementsare aluminum 2-9 per cent, zinc 0.5 to 3 per cent, manganese 0.1 to 0.5percent. The presence in the alloy of 0.05 to 0.5 per cent of calcium isalso desirable. The anode material may be in any of the forms in whichmagnesium articles may be produced, such as rod, sheet. plate, and thelike.

The electrolyte comprises an aqueous solution of ammonium bromide. Theconcentration does not appear to be critical and may range from about 30grams per liter to amounts producing nearly saturated solutions. Agenerally useful range of concentration is between about and 300 gramsper liter, 200 grams per liter being preferred.

For some purposes. as when the .cells are to remain for long periods onopen circuit or are to be used intermittently over long periods, it isdesirable to reduce the rate at which the anode material is corroded bythe electrolyte. This may be accomplished by including in theelectrolyte a chromic acid salt of a base of the alkali, alkaline earth,and ammonium bases, such as NafCrO4 or NazCrzOfr. Li'zCrOa. or LiyCrzOv,CaCrO4 0r CaCrzO'l, (NH4) zCrO'4 0r (NH4) 2CrzO1 for example, incorrosion-inhibiting concentrations such as from about 0.01 to 25 gramsper liter of solution.

The cathodes used according to the invention are similar to thoseheretofore used in standard Leclanch cells. They consist of carbon rodsor plates or other suitable form of the material embedded in adepolarizer mass consisting of a v mixture of manganese dioxide andfinely divided in which the anode is separated from the cathode and theelectrolyte provides a path for the passage of electrical currentbetween them as in conventional cell construction.

The invention may be further explained and illustrated with reference tothe aforesaid draw- Fig. 1 of the drawing represents a .wet cellassembled in accordance with the invention, cut

away to show internal structure. A container or 3 jar I of insulatingmaterial, such as glass or molded plastic, is divided into' an anodecompartment 2 and a cathode compartment 3 by means ofa partition 4.Partition 4 consists of a board or plate of insulating material, such asglass or plastic, which is conveniently molded of phenol-formaldehyderesin. It is provided with a plurality of perforations 5, arranged in aregular pattern, to permit the passage of current through theelectrolyte between the electrodes. On the cathode side of partition 4is a porous illter medium 6 such as a sheet of filter paper, whichserves as a liquid-permeable retainer for the contents of the cathodecompartment. In compartment 2 is disposed an anode 1 consist- .ing of aplate of magnesium to which is secured ous solution of ammonium bromideto which may be added, if desired, corrosion-inhibiting amountsof achromic acid salt of an alkali metal, alkaline earth -metal or ammonium.Cathode I3 in compartment 3 is a carbon rod having terminal I I, whichis embedded in a mass I2 of a depolarizer mix composed of manganesedioxide and nely divided carbon moistened with the electrolyte.

The dry" lcell shown in Fig. 2 comprises the container 2|, which is acup formed of magnesium and serves as the anode. Cathode 22 is a carbonrod with terminal cap 23, packed in a bobbin 24 of depolarizer mass ofmanganese dioxide and carbon moistened with an electrolyte of the samecomposition as that already mentioned. Between depolarizer 24 and thesides of the cup is a body of gelled electrolyte 25. An insulating disc26 of waxed paper, paper board, or the like separates the depolarizerbobbin from the bottom of the cup 2|, and a similar disc 21 covers thetop of the bobbin. A vent space 28 is provided above disc 21, which isclosed by a vented insulating cover 29 of wax or resin.

TABLE I D size dry cells Electrclyte, Grams per Liter Capacity FlashLight Test- Days to 0.935 Volt Cell Hours' N o. Continu- Salt Inhibitorcus Discharge to 1.13 Volt Examples of primary cells made in accordanceY with the invention and of the design shown in Fig. 2 are set forth inTable I. In Table I the cells were conventional D size (ilash lightcells) "dry cells. Cells numbered 1 to 18 inclusive employed as theanode material a magnesiumbase alloy having the nominal composition: 3per cent A1, 1 per cent Zn, 0.2 per cent Mn, remainder vper 120 c. c.of' solution. The cathodes of each cell consisted of a carbon rod packedin a depolarizing mass composed of per cent by weight MnOz (gold coastore) and 10 per cent acetylene black moistened with the electrolyte. Thecells were subjected vto two capacity tests. 'I'he one, Hours continuousdischarge, consisted in determining the number of hours required for thecell voltage to drop to 1.13 volts on being continuously dischargedthrough a resista'nce of 831/3 ohms. The other, Flash light test,consisted in determining the number o1' elapsed days for the cellvoltage to drop to 0.935 volt when discharged through a resistance of 6%ohms for 4 minutes of each V2 hour through 10 hours of each day for 5days a week.

Wet cells made up in accordance with the invention and of the designshown in Fig. 1 are set .forth in Table 1I. The cells held 300 c. c. ofelectrolyte of the composition indicated in Table II and the anodes wereplates 31/2" x 2" x 1A" of the composition indicated. In the table, M1is the A. S.' T. M. designation of a magnesiumbase alloy having thenominal composition of 1.5 per cent manganese, the balance commercialmagnesium; AZ31 is the A. S. T. M. designation oi' a magnesium-basealloy whose nominal composition is: 3 per cent aluminum, 1 per centzinc, 0.3 per cent manganese, remainder commercial magnesium. Thecathode mix in the cathode compartment consisted of 90 per cent byweight of manganese dioxide (gold coast ore) and 10 per cent ofacetylene black. In determining the capacity of these cells they weredischarged through a resistance which was adjusted to a value such thatthe current density initially was 6 amperes per square foot of anodesurface facing the cathode compartment. ampere hours produced by thecell discharging through the said resistance until the voltage droppedto 1 volt was measured and is set forth in the last column.

In operation, cells made according to the invention constitute a uniquevoltaic system inasmuch as the cathode is depolarized by manganesedioxide which operates in an alkaline medium. Very soon after current isdrawn trom the cells it is found that the pH initially at about 6.6quickly enters the range of about 7.5 to 8.3, the latter pH being themaximum attained. Within this pH range most of the energy of the cell isdelivered. Attempts heretofore to utilize manganese dioxide as adepolarizer in an aqueous alkaline medium have been unsuccessful. For

The number of y example, the zinc Leclanch cell becomes useless when theelectrolyte becomes alkaline, due to the resulting drop in voltage ofthe cell. In contrast with this, in operation the electrolyte of ourcells exhibits a pH of about 7.5 to 8.3, a pH range at whichconventional cells using a manganese dioxide-depolarized cathode do notfunction.

It is to be understood that the foregoing description is illustrativerather than strictly limitative, and that other embodiments of the newcell are possible within the spirit of the invention and the scope ofthe following claims.

We claim:

1. A primary cell comprising a magnesium anode, a manganesedioxide-depolarized cathode, and an electrolyte comprising an aqueoussolution of ammonium bromide.

2. A primary cell comprising a magnesium anode, a manganesedioxide-depolarized cathode, and an electrolyte comprising an aqueoussolution of ammonium bromide, and corrosion-inhibiting amounts of achromic acid salt of a base selected from the group consisting of thealkali metal, alkaline earth metals, and ammonium bases.

3. A primary cell comprising an anode of a magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, the balance being magnesium, amanganese dioxide-depolarized cathode, and an electrolyte comprising anaqueous solution of ammonium bromide.

4. A primary cell comprising an anode of a. magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, 0.05 to 0.5 per cent of calcium,the balance being magnesium, a manganese dioxide-depolarized cathode,and an electrolyte comprising an aqueous solution of ammonium bromide.

5. A primary cell comprising an anode of a magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, the balance being magnesium, amanganese dioxide-depolarized cathode, and an electrolyte comprising anaqueous solution of ammonium bromide, and corrosion-inhibiting amountsof a chromic acid salt of a base selected from the group consisting ofthe alkali metal, alkaline earth metals, and ammonium bases.

6. A primary cell comprising an anode of a magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, 0.05 to 0.5 per cent of calcium,the balance being magnesium, a manganese dioxide-depolarized cathode,and an electrolyte comprising an aqueous solution of ammonium bromide,and corrosioninhibiting amounts of a chromic -acid salt'of a baseselected from the group consisting of the alkali metal, alkaline earthmetals, and ammonium bases.

7. A primary cell comprising a magnesium anode, a manganesedioxide-depolarized cathode, and an electrolyte comprising an aqueoussolution of ammonium bromide, and corrosion-inhibiting amounts ofammonium chromate.

8. A primary cell comprising an anode of a magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, the balance being magnesium, amanganese dioxide-depolarized cathode, and an electrolyte comprising anaqueous solution of ammonium bromide, and corrosion-inhibiting amountsof ammonium chromate.

9. A primary cell comprising an anode of a magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, 0.05 to 0.5 per cent of calcium,the balance being magnesium, a manganese dioXide-depolarized cathode,and an electrolyte comprising an aqueous solution of ammonium bromide,and corrosioninhibiting amounts of ammonium chromate.

l0. A primary cell comprising a magnesium anode, a manganesedioxide-depolarized -cathode, and an electrolyte comprising an aqueoussolution of ammonium bromide, said electrolyte having a pH between about'7.5 and 8.3.

11. A primarycell comprising an anode of a magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, the balance being magnesium, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of ammonium bromide, said electrolyte having a pHbetween about 7.5 and 8.3.

12. A primary cell comprising a magnesium anode, a manganesedioxide-depolarized cathode, and an electrolyte comprising an aqueoussolution of ammonium bromide, and corrosionnhibiting amounts of ammoniumchromate, said electrolyte having a pH between about 7.5 and 8.3.

13. A primary cell comprising an anode of a magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 percent ofzinc, 0.1 to 0.5 per cent of manganese, the balance being magnesium, amanganese dioxidedepolarized cathode, and an electrolyte comprising anaqueous solution of ammonium bromide, and corrosion-inhibiting amountsof ammonium chromate, said electrolyte having a pH between about 7.5 and8.3.

14- A primary cell comprising an anode of a. magnesium-base alloycontaining from about 2 to 9 per cent of aluminum, 0.5 to 3 per cent ofzinc, 0.1 to 0.5 per cent of manganese, 0.05 to 0.5 per cent of calcium,the balance being magnesium, a manganese dioXide-depolarized cathode,and an electrolyte comprising an aqueous solution of ammonium bromide,and corrosioninhibiting amounts of ammonium chromate, said electrolytehaving a pH between about 7.5 and 8.3.

ASHFORD B. FRY. ROY C. KIRK. PERCY F. GEORGE.

REFERENCES CITED The following references are of record in the *le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,521,295 Holler Dec. 30, 19242,343,194 Lawson Feb. 29, 1944

1. A PRIMARY CELL COMPRISING A MAGNESIUM ANODE, A MANGANESEDIOXIDE-DEPOLARIZED CATHODE, AND AN ELECTROLYTE COMPRISING AN AQUEOUSSOLUTION OF AMMONIUM BROMIDE.